I've run a DH, Barb, and Monk so far.
Monk's build was copied from the Monk Cannon thread. My stats are basically what is advertised as needed in the thread. The monk RARELY dies, and when it does, its because its trying to avoid some kind of elemental elite while trying to kill it at the same time, so it runs over fire or arcane a bunch of times trying to dodge and kill at the same time. Other than that, the Monk is incredibly efficient and was VERY cheap to build. He is running MP1 and is paragon 88.
My barb is your standard WW/Sprint barb. His gear is slightly better than the monks gear, which is quite more expensive when its gear for a barb since I can't factor in one with everything like I could on the monk. The barb is incredible to watch bot, he slaughters everything. Its kind of gross. He will also die in situations like I mentioned my monk running into. He also farms MP1 but is not nearly as high of paragon as the monk.
My DH botting experience was pretty crappy, only botted MP0 as it was all she could really handle.
If I were setting up bots, knowing in my head that I needed to turn a quick profit, I would go with a bunch of monks because of the ease of obtaining the correct items needed to bot efficiently. If you can afford it though, the barbarian seems like it would be, overall, the best.